Particle Size Distribution is a vital consideration in almost any powder processing operation. It influences how material moves through company equipment, how it responds to applied force during compaction, how evenly it mixes with other ingredients, and how reliably it performs in its final application. That makes it a priority for powder processing operations across a wide variety of sub-sectors, including pharmaceutical OSD, food and nutraceutical production.
Here, our experts at Quadro take a deep dive into Particle Size Distribution, and examine the various ways in which it can affect your operations. That can help you and your team to identify the underlying causes of any variability in your processes, so that you can have peace of mind in consistent, high-quality end results.
Particle size distribution (PSD) is a statistical representation of the range of particle sizes present within a particulate material, and the proportion of particles that fall within each size range.
It quantifies how particle sizes vary across a powder or particulate system, rather than assuming all particles are identical. The distribution is typically presented as a graph with particle size on the horizontal axis and the percentage of the total sample on the vertical axis.
The key metrics of PSD are numerical values that summarize the distribution of particle sizes. They help engineers and formulators compare powders, assess consistency, and make process adjustments to meet product requirements. Crucially, these metrics can provide insight into flow behavior, compaction, dissolution, and mixing efficiency.
They are as follows:
As well as the above, another key metric within particle size distribution is span.
Span is a metric used to quantify the width of a particle size distribution. It compares the distance between the smaller and larger particle percentiles relative to the median particle size, which enables engineers to quickly judge how broad or narrow each distribution is.
There are several reasons why this is important - for example, the width of the distribution can influence properties like powder flow, mixing behavior, compaction, and dissolution.
Span is calculated using the formula (D90 − D10) / D50, which uses the percentile particle sizes to express how wide the distribution is relative to the median particle size. A larger span value indicates a wider distribution of particle sizes, while a smaller span value indicates a tighter and more uniform distribution.
Spread is very distinct from span in particle size distribution, although it can be easy to get them confused. Spread refers to how wide or narrow the range of particle sizes is within a material. It shows how far apart different portions of the particle population are, and can be interpreted by comparing values such as D10 and D90, or by using span to quantify the distribution width.
In terms of spread, particle size distribution is often described as either broad or narrow.
Broad PSD - A broad PSD contains a wide range of particle sizes, and is typically indicated by a large difference between D10 and D90 or a higher span value. In some systems, smaller particles can fill the gaps between larger ones, which may improve powder flow. However, broad distributions can also increase the risk of segregation in certain blends, or lead to uneven compaction.
Narrow PSD - A narrow PSD contains particles within a tighter size range - it’s usually indicated by a smaller difference between D10 and D90 or a lower span value. This can produce more consistent behavior during processing and improve uniformity in manufacturing operations like compaction or dissolution.
Particle size distributions can also be characterized by their shape, which is distinct from their spread. While spread and span refer to the width of the particle size distribution, the type refers to how the particle sizes are grouped within that range.
Powders can have monomodal distributions, where one particle size dominates the sample, or bimodal distributions, where two distinct particle size populations are present. Monomodal distributions generally lead to more consistent compaction and flow, while bimodal distributions may be used to optimize packing density, blend homogeneity, or dissolution rates. The distribution type can be useful in predicting powder behavior and choosing appropriate processing methods.
There are several PSD measurement methods to choose from. The best choice often depends on the powder type, particle size range, and required level of precision.
When it comes to choosing the technique that’s best suited for your own operations, there are a couple of key factors you’ll need to take into account. This includes the properties of the material (such as its hardness, friability, or moisture), any relevant regulatory requirements, and the scale of the operation in question (lab, pilot or production).
If you need assistance, Quadro’s Waterloo Technology Centre can provide comprehensive testing services to ensure the accuracy of your measurements, and applicability for specific processes.
| Sector / Application | Why is PSD so important? |
| Pharmaceutical OSD | Tablet compaction, dissolution, content uniformity, and bioavailability all depend on tight PSD control |
| Pharmaceutical API | API particle size affects solubility, bioavailability, and downstream formulation compatibility |
| Wet Granulation | PSD at each stage (pre-mill, wet mass, dry calibration) determines final granule quality and tablet press performance |
| Nutraceuticals | Consistent PSD ensures accurate dosing, improved mouthfeel, and product uniformity |
| Food Manufacturing | PSD affects texture, flavour release, solubility, and consumer experience |
| Chemical Processing | PSD impacts reaction rates, product purity, handling safety, and formulation consistency |
There’s a range of variables that can alter particle size distribution during powder processing. These changes largely affect how the powder behaves in manufacturing operations such as flow, blending, and compaction.
These include:
Milling method and equipment type - Cone milling, jet milling, and hammer milling produce different PSD profiles, which can impact product behavior.
Screen selection - Hole size, shape (round, square, grater), and thickness can influence the maximum particle size exiting the mill.
Impeller speed and tip velocity - Higher speeds can produce finer PSDs but may generate heat or fines.
Feed rate and material characteristics - Hardness, moisture content, bulk density, and friability can all influence the resulting PSD.
Pre-conditioning - Security screening and delumping before milling (e.g., with the FlexSift) can help to ensure a more uniform feed and protect downstream equipment, which can improve overall process consistency.
The ability to achieve a controlled Particle Size Distribution is largely dependent on the precision with which a milling system is able to manage particle breakage and classification during processing. At Quadro, our cone milling technology effectively addresses this requirement by giving your engineers direct control over the key milling variables that determine PSD.
It does this through three core parameters:
Each of these variables influences how material interacts with the milling chamber - screen selection determines the maximum particle size that leaves the mill, while the impeller profile controls how the material moves through the screen surface. Finally, tip speed then governs the intensity of the particle size reduction.
Together, these factors help to create a predictable milling environment that can help your team to generate repeatable PSD outcomes, fulfilling your formulation requirements and downstream processing needs.
Our cone milling range provides this level of control across laboratory, pilot, and production environments:
What’s more, this scalable approach means that your PSD targets can remain consistent as your process moves from early formulation through to full manufacturing. If you ever need to validate PSD performance with real materials, our Technology Centre offers collaborative process trials. Here, your team can work with Quadro product and application specialists to test equipment configurations and process parameters, and observe the resulting particle size outcomes.
Find out more about our Waterloo Technology Centre.
There is no single ideal D50 for tablet manufacturing because the optimal powder particle size depends on the formulation, excipients, and processing method. Many tablet formulations fall within a typical range of roughly 50–300 µm, but the correct value is determined by how the powder flows, blends, and compacts during processing.
No. A narrow PSD can improve consistency in processes such as compaction or dissolution, but it’s not always optimal. In some formulations, a broader or bimodal distribution may improve packing density or flow by allowing smaller particles to fill the spaces between larger ones.
Yes, to a degree. PSD can be influenced during manufacturing through equipment selection, milling parameters, screen size, and feed conditions. However, material properties and upstream processing steps also affect the final distribution, so control typically involves managing several process variables rather than a single adjustment.
D10, D50, and D90 are percentile values used to describe a particle size distribution. D10 is the particle size below which 10% of the particles are found, D50 is the median particle size, and D90 is the size below which 90% of the particles occur. Together they help to illustrate the range and spread of particle sizes within a material.
Whatever sub-sector you work in, PSD is always going to be a key consideration. Its ability to influence the behavior of a material means that it can strongly influence the final appearance and quality of your products, whether you’re manufacturing tablets, processing API, or running wet granulation.
In terms of maintaining the consistency of your PSD, some of the most crucial factors that help to do so include the quality and suitability of your screening equipment, and fine-tuned control over your process parameters. That’s exactly where we can help here at Quadro. Our equipment and application experts can help you define, achieve, and maintain your target PSD - from lab to production scale.
Get in touch today to talk to our team about the best solution for your requirements.